The present invention relates to inflators for vehicle airbags and, more particularly, to a linear inflator which discharges inflation gas along the length of the inflator for use in side impact or head curtain airbag systems.
Due to airbag module size restrictions, it is desirable to pack as much gas generant as possible in a given volume of an inflator combustion chamber. However, linear inflators used in side impact or head curtain airbag systems should be loaded with a consistent and uniformly distributed mass of gas generant to help ensure a constant propagation rate of the combustion reaction along the inflator and to help ensure generation of a relatively constant and predictable gas pressure within an associated airbag. This is because the total volume of gas generated and the mass flow rate of the gas generated will vary based on the void volume (i.e., volume not occupied by gas generant) in the combustion chamber. In addition, if too little void volume is provided in a linear inflator, inflation gas flow will be restricted, resulting in a high operating pressures and possible mechanical failure of the inflator. Also, the time between first ignition of the gas generant at a first end of the linear inflator and combustion of the final portion of gas generant at an opposite end of the inflator (i.e., the combustion propagation time) is very important. This propagation time is dependent upon the overall void volume within the combustion chamber and the distribution of the void volume along the combustion chamber.
In inflator designs having a combustion chamber with a relatively small diameter and relatively large length, it may be difficult to provide the desired uniform distribution of gas generant along the combustion chamber. Although an extrudable gas generant could be used, it is often desirable to use a gas generant that is produced on a rotary tablet press. However, the positioning and orientation of gas generant tablets in a long, narrow combustion chamber introduces unique problems with regard to uniformity of gas generant distribution.